The unclued lights (one of two words) can be resolved into three associated trios which are not the solution to the problem. Solvers have to search the completed grid and then highlight the trio which does so.
 

Across

11    Maigret’s sidekick has read case in French (5)
12    Those in the band that take some beating (5)
15 The military can stand this (6, two words)
16    Is he blotto permanently? Only partly (5)
17    It’s about time, note, for repeats (8)
18    Larks start to sing after peace’s shattered around outskirts of Ashtead (9)
20    Pierrepoint’s letter game (7)
23    Additional luxurious fabric is cut (4)
25    Stupid person lacking emotion, twisted inside (4)
26    Principles suggest ‘ring after eleven in the mornings’ (6)
28    Ledge bearing mothball (6)
29    Collaborator’s friendly, but wanting power (4)
31    Roll up from some distance (4)
33    Country article left Spice Girl slightly abashed (7)
34    Choice about time for surgery (9)
37    The Spectator is forward with beautiful woman (8)
39    Basket case’s beginning to stagger (5)
42    Antique fellows you may see on the coast (5)
43    Relatives like holding posh books (5)
44    Steadfast belief, whichever way you look at it (5)
45    Freelances — as a char? (6)
46    Criminal’s offspring is going into painting (8)
 

Down

1    Discolorations or blemish over half the county (8)
2    Luminous phenomena — distinctive characters containing gold (7)
3    Slow to get a kiss, the sap! (5)
4    Evens? Maybe. Maybe not (4)
7    Like carrier, off course (6)
8    Said ‘Super’ which does jar! (5)
9    Some licensees’ measures (3)
10    This factor’s macaque (6)
19    Where some, oddly, imbibe alcohol in Massachusetts? (5)
21    Old vessels having much capacity out east (8)
22    Greeting everyone in house (5)
24    Look at the posh car that’s going after other vehicles (7)
29    Feeler, as before, to which the woman rises (7)
30    Invest in lots of paper, it’s said, for ancient craft (7)
31    French police stripped for some entertainment (6)
32    Sinking right into marsh, an outdoor shoe (6)
35    Wisp of smoke from chimney in Peterborough (5)
38    Bully makes withdrawn son cry (4)
41    Hooter from crumpled front of Wolseley (3)
 
A first prize of £30 for the first correct solution opened on 1 May. There are two runners-up prizes of £20. (UK solvers can choose to receive the latest edition of the Chambers dictionary instead of cash — ring the word ‘dictionary’.) Entries to: Crossword 2305, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.